The prior art evidences attempts to provide a satisfactory coupling device for coupling optical energy traveling in optical fibers to thin-film optical waveguides. For instance, see "Interconnection of Optical Fibers to Planar Optical Integrated Circuitry," by Ash et al., appearing in IBM Technical Disclosure Bulletin, Volume 13, No. 9, pages 2529-30 (Feb. 1971). Another example of a device which is capable of coupling optical energy from an optical fiber to a thin-film waveguide is disclosed by Lean et al., in U.S. Pat. No. 3,791,715.
Although the devices referred to above may adequately couple optical energy from an optical fiber to a planar waveguide it is desirable to provide an improved coupler which meets one or more of the following criteria.
Reference to the Ash et al disclosure will illustrate that it is based on periodic structures setting up an interference pattern to cause a coupling of optical energy from a fiber to the waveguide. One of the difficulties with this approach is that it requires extremely accurate photolithography in order to transfer a pattern from a mask to a waveguide. Some of the mechanical handling requirements for performing the Ash et al. methods also do no admit of easy solution; for example, laying a fiber optic bundle along a planar waveguide with an included angle of approximately 1.degree. is a difficult task, at best.
Another approach, such as that disclosed by Lean et al. requires the presence of electrical energy in order to "open" the coupler so that it will pass optical energy from the fiber optic to the planar waveguide. Another characteristic of Lean et al. which it may be desirable to omit is the necessity for coupling the light waves through the atmosphere, as is illustrated in FIG. 1 of Lean et al.
The foregoing disadvantages, and others, are typical of the prior art which can generally be characterized as requiring critical positioning and angular alignment of the fiber with respect to the waveguide substrate which makes manufacture of the coupler difficult.